traingular numbers can be modeled by a function suggested in the diagram. if you duplicate each triangular number on top of itself, you can partition the resulting arrangement into an n by square and a 1 by n now. Graph the function f(n)=1/2(n^2+n) and y=91 to determine which triangular number 91 is. Use your graph to communicate why any intersection points may be a solution to the equation, but now a reasonable solution to the problem.